jgmenu: add update script

pkgs/applications/misc/jgmenu/default.nix

@@ -11,6 +11,7 @@
 , enableXfcePanelApplet ? false
 , xfce
 , gtk3
+, gitUpdater
 }:
 
 stdenv.mkDerivation rec {
@@ -57,6 +58,8 @@ stdenv.mkDerivation rec {
     done
   '';
 
+  passthru.updateScript = gitUpdater { rev-prefix = "v"; };
+
   meta = with lib; {
     homepage = "https://github.com/johanmalm/jgmenu";
     description = "Small X11 menu intended to be used with openbox and tint2";